Field of the Invention
The invention relates to a method for demodulating an analog receive signal carrying information as well as a corresponding demodulator for carrying out the method. The technical field of the invention is in the area of information transmission in wireless and wired transmission systems. The invention may be used, in particular, in mobile radio systems for communication, in systems for satellite-based position determination (for example, in GPS or Galileo systems) as well as in WLAN networks, in wireless or wired radio, TV or Internet networks as well as for radar and sonar applications and for radiodetermination. In particular, the invention deals with the object of demonstrating, for the receiver side of a transmission path, a way to rapidly and yet energy-efficiently process receive signals which carry a high information density and have a large bandwidth.
Description of the Background Art
In conceptualizing and developing communication and measurement systems, it is desirable to achieve high data rates and a high measuring accuracy. In mobile receiving devices, in particular, a compromise must be reached between technical complexity, price, physical power and energy consumption. Analog-digital conversion (AD conversion) on the receiver side for digital further processing of the information signal, in particular, is a key component with regard to complexity and power efficiency. The analog information signal must be both time-discretized and limited to a finite, digital word width. A digitization method using a high word width results in complex analog circuits, which are limited in speed and also have a high power consumption. This is an obstacle, particularly when using broadband signals (e.g., the ultra-broadband technology, abbreviated as UWB), since fast sampling rates are needed here for the purpose of distortion-free reception.
The method of so-called time interleaved AD conversion (TI-ADC) is one option for sampling receive signals having a high word width without having to compromise on the sampling rate, wherein an existing analog signal is not converted by an individual AD conversion at the desired sampling rate but by a large number of converters, each of which works at a rate which is lower than the desired sampling rate. The receive signal is applied to the inputs of the parallel AD converters for this purpose. These converters sample the signals with a time shift at a reduced sampling rate in each case. The digital signals of the individual converters are then combined by a multiplexer to form the desired digital output signal.
The resulting digital output signal of the TI-ADC ideally corresponds to the signal generated by a conversion using a single converter of the desired high sampling rate. Overall, a sampling rate may thus be achieved, which is higher than the possible sample rates of the individual converters. A TI-ADC method is known, for example, from US 2011/0244811 A1. In this publication, according to the exemplary embodiment illustrated in FIG. 2, a receive signal is distributed to two AD converters, the second converter sampling the receive signal, phase- and thus time-shifted by 90° with respect to the carrier frequency.
In practice, however, multiple AD converters are unable to sample the receive signal, precisely synchronized at an offset from each other. High resolution AD converters are also unable to be implemented with the same design in terms of their real properties. In a TI-ADC method, therefore, synchronization errors as well as different threshold voltages and amplification factors of the individual AD converters must be disadvantageously estimated and compensated for after the digitization adding to the complexity.